Opaque polymeric films in which the opacifying agent is finely divided polymer dispersed in the continuous film polymer phase are described in U.S. Pat. Nos. 4,368,295 and 4,377,616, which are incorporated herein by reference in entirety. U.S. Pat. No. 4,368,295 discloses opaque polyester films containing dispersed polypropylene and a carboxylated polyethylene additive.
In U.S. Pat. No. 4,377,616, a film is prepared by melting a mixture of a major proportion of a film forming polymer such as polypropylene and a minor proportion of an incompatible polymer which has a higher melting point, at a temperature sufficient to melt the incompatible polymer and to dispense it in the film forming polymer, extruding the mixture into a film and biaxially orienting the film. The dispersed incompatible polymer provides sites for the formation of voids surrounding the dispersed polymer particles. These voids provide opacity and give the film an attractive pearlescent sheen. Reduction of the size of the dispersed particles and reduction of the occurrence of stringiness in those particles, as sometimes occurs, results in a film having improved opacity and better appearance. Such improvements are provided in accordance with this invention.